Process for the removal of small quan-



United States Patent F PROCESS FOR THE REMOVAL OF SMALL QUAN- TITIES OF ORGANIC ACIDS FROM MONO- MERIC VINYL =ESTERS Gerhard Hiibner, Burghausen, Upper Bavaria, Germany,

'assignor to Wacker-Chemie G.m.b.H., Munich, Germany No Drawing. Filed Jan. 23, 1959, Ser. No. 788,484 Claims priority, application Germany Apr. 3, 1958 2 Claims. (Cl. 260-4103) The present invention relates to an improved process for the removal of small quantities of organic acids from monomeric vinyl esters.

'In the production of vinyl esters from higher fatty acids, first runnings and last runnings are always obtained which are contaminated with small quantities of fatty acids. In View of their similar boiling points they cannot be completely separated from the vinyl esters by distillation. The fact that generally the fiactionation must be carried out at reduced pressures renders the situation especially diflicult. For example, in the production of lauric acid vinyl ester, whose boiling point at 4 mm. Hg pressure is 123 C., the presence of capric acid and caprylic acid must be reckoned with, whose boiling points respectively are 132 C.'andl09 C. at 4 mm. Hg pressure, and in the production of capric acid vinyl ester, Whose boiling point at 50 mm. Hg pressure is 148 C., the presence of caprylic acid and caproic acid, whose boiling points respectively are 159 C. and 135 C. at 50 mm. Hg pressure, must be reckoned with. As it isnot possible to obtain substantially pure vinyl esters fromthe' first running and last running fractions of the contaminated esters even upon repeated distillation, it-was previously'necessary to remove the acids chemically. 'This, for example, has been accomplished by neutralization, for example, by washing with aqueous alkaline solutions. The soaps produced, however, give rise to emulsions which are difficult to separate. Also, after removal of the aqueous layer from the ester layer, the latter must be dried before distillation, as otherwise acid would again be produced by saponification. The fatty acids can only be recovered from the aqueous layer by boiling with equivalent quantities of mineral acids.

The disturbing acids can also be removed with the aid of anion exchangers. This method, however, is rather costly as in regeneration of the ion exchange columns very dilute alkaline soap solutions are obtained which must be treated with comparatively large quantities of mineral acid to recover the fatty acids.

A further but not commercially feasible method is to convert the vinyl ester into a complex by treatment with a three-fold quantity of urea and a twenty-fold quantity of methanol.

According to the invention it was found that the or ganic acids can be removed from the vinyl esters and recovered in the distillation retort without necessitating additional apparatus and with only little expenditure of chemicals, time and work. In the process according to the invention the acid containing vinyl ester is heated to 80-150 C. in the presence of a small quantity of sulfuric acid and the acid free vinyl ester separated therefrom by distillation without neutralization of the sulfuric acid. The quantity of sulfuric acid employed is at least 0.01% and preferably does not exceed 1% based upon the acid containing vinyl ester. The introduction of an inert gas, such as nitrogen, or stirring promotes the reaction.

2,986,575 Patented May 30, 1961 2 The fatty acids are set free from the distillation residue, consisting of ethylidene diesters and fatty acid anhydr'ides, by acid saponification using known methods, such as, for example, by steam distillation.

The sulfuric acid which is added to the contaminated vinyl esters acts as the catalyst for both reaction steps, namely, for the conversion of the organic acid into higher boiling products and for the saponification of such higher boiling products. Instead of pure sulfuric acid, mixtures of such acid with other acids can be employed. Preferably, the sulfuric acid is added to the vinyl ester in dilute form in an inert diluent, as the introduction of concentrated sulfuric acid tends to lead to resinification of the vinyl ester at the point of admixture.

The process according to the invention is not only applicable for the purification of vinyl esters of higher fatty acids. It is, to the contrary, possible to free every organic vinyl ester from organic acids by such process. However, the problems indicated above in general only occur in the case of vinyl esters of fatty acids containing 6-18 carbon atoms. The process according to the invention is most expediently applied to vinyl esters contaminated with up to 10% of free fatty acids.

When vinyl esters contaminated with fatty acids are employed directly for polymerization and copolymerization without removal of the fatty acids, undesirable effects would be produced, such as, for example, corrosion and unpleasant odors.

The following exampleswill serve to illustrate several embodiments of the process according to the invention.

Example 1 1400 g. of a vinyl laurate first runnings containing 5.2% of fatty acid (calculated as lauric acid) were admixed with a mixture of 0.8 g. concentrated sulfuric acid and 5 g. of lauric acid (as diluent for the sulfuric acid). The mixture was heated for 5 hours at 120 C. and then distilled under a pressure of 2 mm. Hg. 102 g. of first runnings containing 1.7% of acid distilled over at -103 C., 1.140 g. of the main fraction containing 0.5% of acid distilled over at 103 -105 C. The distillation residue amounted to 155 g.

When an analogous distillation of the contaminated vinyl ester was carried out in the same distillation column (10 theoretical plates) but without pretreatment with sulfuric acid, 290 g. of first runnings containing 7.7% of acid, 1020 g. of main fraction containing 3.6% of acid and g. of residue were obtained.

Example 2 800 liters of vinyl laurate first runnings containing 8.8% of acid were mixed with 40 cc. of concentrated sulfuric acid dissolved in 5 liters of lauric acid. The mixture was then heated to C. while passing nitrogen therethrough. The course of the reaction was followed by determination of the acid content which is given in the following table:

Acid content, percent After addition of catalyst 9.9 After 1 hour at 120 C. Z 7.8 After 2 hours at 120 C. 6.0 After 3 hours at 120 C. 5.4 After 4 hours at 120 C. 4.4 After 7 hours at 120 C. 1.0

I 3 The acetaldehyde which was produced simultaneously went over into the water layer.

Example 3 Atest' mixture of 475 g. of caprylic acid vinyl ester and 25 g. of caproic acid was fractionated at a pressure of 1.2 mm. Hg over a column theoretical plates). The fraction which distilled over between 67 and 68 C. amounted to 464 g. and contained 4.1% of caproic acid. The residue in the still contained 7.4% of caproic acid.

When such test mixture was first admixed with 0.6 g. of concentrated sulfuric acid and heated for 1 hour at 110 C. before such distillation the fraction going over at 6768 C. contained 0.8% of caproic acid and amounted to 451 g. The residue contained 2.0% of free ca'proic acid.

Example 4 An essentially pure commercial vinyl stearate having a 1% acid content (calculated as stearic acid) was admixed with stearic acid to raise the total acid content to 2% and divided into two parts. One half was mixed with 0.2% of phenothiazine as a polymerization inhibitor and distilled in a Claisen distilling flask at a pressure of 0.1 mm. Hg. 45 g. of ester were distilled ofl? from the 50 g. of the mixture introduced. The stearic acid content of the distilled ester was 1.2%.

The other half was mixed with 0.05% of sulfuric acid and heated for three hours on a boiling water bath. 50 g. thereof were then mixed with 0.1% of phenothiazine andthen distilled as described above. 44 grams of ester with an 0.5% acid content were obtained.

Example 5 1% of myristic acid was admixed with commercial vinyl stearate. The total acid content in such mixture calculated on the average molecular weight of the acids was 1.75%. 0.1 g. of phenothiazine was added to 50 g. of such mixture and the mixture distilled over a Claisen distilling flask at a pressure of 0.1 mm. Hg. 45 g. of distillate containing 1.4% of acid were obtained.

When the same mixture was first given a three hours pretreatment with 0.05% of sulfuric acid on a boiling hot 4 water bath and then distilled in the same manner, grams of ester with a 0.3% acid content were obtained.

Example 6 Crude vinyl caprate, which was produced from technically pure capric acid, upon distillation in a column with 24 theoretical plates under a pressure of 2 mm. Hg produced a main fraction with a constant acid content of about 6%. The acid content of this fraction could not be reduced even upon a sharp refractionation. It was a constant boiling mixture of vinyl caprate and caprylic acid. The caprylic acid was derived from the technical capric acid which contained about 4% thereof as an impurity.

700 liters of the twice distilled ester having an acid content of 6% were admixed with a solution of 350 cc. of concentrated sulfuric acid in 8 liters of lauric acid and the mixture then heated to C. for three hours. Distillation of the thus pretreated vinyl ester at 2 mm. Hg pressure produced 580 liters of vinyl caprate containing 0.4% of acid.

I claim:

1. A process for the removal of organic acids from vinyl esters which comprises heating a vinyl ester containing up to about 10% of organic acid as an impurity in the presence of 0.01% to 1.0% of sulfuric acid based upon the acid containing vinyl ester to a temperature between 80 and C. until a substantial quantity of the organic acid impurity has been converted into a higher boiling product and then distilling the vinyl ester off from the reaction mixture in the presence of the sulfuric acid.

2. The process of claim 1 in which the vinyl ester treated is a vinyl ester of a higher fatty acid containing up to 10% of a higher fatty acid as an impurity.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR THE REMOVAL OF ORGANIC ACIDS FROM VINYL ESTERS WHICH COMPRISES HEATING A VINYL ESTER CONTAINING UP TO ABOUT 10% OF ORGANIC ACID AS AN IMPURITY IN THE PRESENCE OF 0.01% TO 1.0% OF SULFURIC ACID BASED UPON THE ACID CONTAINING VINYL ESTER TO A TEMPERATURE BETWEEN 80 AND 150*C. UNTIL A SUBSTANTIAL QUANTITY OF THE ORGANIC ACID IMPURITY HAS BEEN CONVERTED INTO A HIGHER BOILING PRODUCT AND THEN DISTILLING THE VINYL ESTER OFF FROM THE REACTION MIXTURE IN THE PRESENCE OF THE SULFURIC ACID. 